1. Field of the Invention
The present invention relates to a coated cemented carbide cutting tool member (hereinafter referred as xe2x80x9ccoated carbide memberxe2x80x9d) that resists breakage and chipping of its cutting edge for a long period of time during high speed cutting operations not only of usual steel and cast iron but also of difficult-to-machine materials such as stainless steel because of its excellent surface lubricity against work chips.
2. Description of the Background
Coated carbide members are preferably composed of a tungsten carbide-based cemented carbide substrate and a hard coating layer preferably comprising a titanium compound layer including at least one layer of titanium carbide (hereinafter referred to as xe2x80x9cTiCxe2x80x9d), titanium nitride (TiN), titanium carbonitride (TiCN), titanium carboxide (TiCO) and titanium carbonitroxide (TiCNO), and an aluminum oxide (Al2O3) layer and/or aluminum oxide-zirconium oxide composite layer (Al2O3xe2x80x94ZrO2 composite), in which layer zirconium oxide phases are dispersed in the Al2O3 phase as disclosed in Japanese Unexamined Patent Publication No. 57-39168 and No. 61-201778. The hard coating layer is formed preferably by means of chemical vapor deposition and/or physical vapor deposition and has an average thickness of 3 to 30 xcexcm. A coated carbide member having a hard coating layer, wherein the first layer is TiN, the second layer is TiCN, the third layer is TiCNO, the fourth layer is Al2O3 and the fifth layer is TiN, is disclosed in Japanese Unexamined Patent Publication No. 7-328810. These coated carbide members are widely used in various fields of cutting operations, for example, the continuous and interrupted cutting of metal work pieces such as steel and cast iron.
It is well-known that titanium compound layers have a granular crystal morphology and are used in many applications. TiC layers have been used as highly abrasion resistant materials in many applications. TiN layers have been used in various fields such as surface decorative coating because of the beautiful external gold-like appearance of TiN layers. It is known that outermost layer(s) of the hard coating layer of many kinds of coated carbide member are made of TiN because of its nice appearance. In fact, this distinctive appearance makes it possible for machine operators to identify new cutting edges from the cutting edges which are worn. A TiCN layer that has a longitudinal crystal morphology, which is produced by chemical vapor deposition at a moderate temperature range such as 700xcx9c950xc2x0 C. using reaction gas mixture which includes organic cyanide compounds such as acetonitrile (CH3CN), has been known as a highly wear resistant coating layer. This layer was disclosed in Japanese Unexamined Patent Publications Nos. 6-8010 and No. 7-328808.
Al2O3 layer have several different crystal polymorphs, among which alpha-Al2O3 is known as the thermodynamically most stable polymorph, which has a corundum structure. Typical polymorphs of the Al2O3 layer formed by the usual CVD conditions are stable alpha-Al2O3, meta-stable kappa-Al2O3 and amorphous Al2O3. For these Al2O3 layers, crystallographic investigations are widely performed using an X-ray diffraction system which emits Cu K xcex1-radiation having a wavelength of about 1.5 xc3x85. With regard to the alpha-Al2O3 layer, different types of alpha-Al2O3 layers can be formed depending upon the manufacturing conditions employed. These individual alpha-Al2O3 layers have different X-ray diffraction patterns. They have maximum peak intensities at different positions, at any of 2xcex8=25.6 degrees (its preferred growth orientation is in 012 direction), 35.1 degrees (104 direction), 37.8 degrees (110 direction), 43.4 degrees (113 direction), 52.6 degrees (024 direction), 57.5 degrees (116 direction), 66.5 degrees (124 direction) and 68.2 degrees (030 direction). Also for kappa-Al2O3 layers, different types of kappa-Al2O3 layers can be formed depending on the manufacturing conditions employed. They have maximum peak intensities at different positions, at any of 2xcex8=19.7 degrees, 29.4 degrees, 32.1 degrees, 34.9 degrees, 37.3 degrees, 43.9 degrees, 52.6 degrees, 56.0 degrees, 62.3 degrees and 65.2 degrees.
In recent years, there has been an increasing demand for labor saving, less time consuming cutting operations. Accordingly, there is a tendency to require cutting tools which can be generally used in various cutting operations of different work materials. Further, the conditions of these cutting operations have changed to high-speed cutting operations. For coated carbide members, although there are few problems when they are applied in the continuous or interrupted cutting of alloyed steel or cast iron under common cutting conditions, there are severe problems when they are applied to extremely viscous work materials such as stainless steel or mild iron. Because the chips of these materials generated by the cutting operation have high affinity to conventional Al2O3 layers and Ti compound layers, which comprise a hard coating layer, the work chips are likely to smear tightly against the surface of the cutting edge. These phenomena become more evident at increased cutting speeds and induce the breakage or chipping of the body at its cutting edge with the consequence that the tool lifetime become shorter. A need, therefore, continues to exist for coated carbide members which resist chipping during high speed cutting operations over long periods of time.
Accordingly, one object of the present invention is to provide a coated carbide member which resists breakage or chipping of its cutting edge over long periods of time during high speed cutting operations, not only of the usual steels and cast irons, but also of hard-machining materials such as stainless steel and mild steel.
Briefly, this object and other objects of the present invention as hereinafter will become more readily apparent can be attained by a coated cemented carbide cutting member for a cutting tool comprising a substrate and a hard coating layer on said substrate,
wherein the hard coating layer comprises at least one layer selected from the group consisting of titanium carbide, titanium nitride, titanium cabonitride, titanium carboxide, titanium carbonitroxide, aluminum oxide, and aluminum oxide-zirconium oxide composite in which zirconium oxide phases are dispersed around ground aluminum oxide phases, and
wherein the hard coating layer is provided with an outer layer which comprises titanium oxide which is expressed by the molecular formula TiOw, wherein w is the atomic ratio of oxygen to titanium which ranges from 1.20 to 1.90. The outermost layer has an attractive external appearance and also exhibits excellent surface lubricity against work chips. This coated carbide member provides good wear resistance and long tool lifetime even when used in high speed cutting operations of viscous materials such as stainless steel and mild steel.